<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    div {
        position: absolute;
        left: 0;
        width: 100px;
        height: 100px;
        background-color: pink;
    }
</style>

<body>
    <div></div>
    <script>
        var div = document.querySelector('div');
        var timer = setInterval(function() {
            if (div.offsetLeft >= 400) {
                clearInterval(timer);
            }
            div.style.left = div.offsetLeft + 5 + 'px';
        }, 30);
    </script>
</body>

</html>